1. Field of the Invention
The present invention relates to an information transmission and reception system for a vehicle which supplies information from any vehicular information source, such as switches, sensors and so on, to a vehicle information receiver which makes use of that information from the information source such as warning indicators, and normal loads such as headlights, etc.
2. Description of the Prior Art
In conventional transmission and reception systems applied to vehicles, electrical connections between vehicle information sources, such as switches and sensors, and vehicle information handling parts, such as loads and indicators, have always been in a one-to-one relationship with wire harness.
FIG. 1 shows a conventional transmission and reception system applied to the vehicle as described above.
As shown in FIG. 1, the vehicle is divided into an engine compartment denoted by &lt;ENG.&gt;, a dashboard central section denoted by &lt;DASH&gt;, an instrument panel denoted by &lt;INST&gt;, and a trunk denoted by &lt;TRUNK&gt;.
The engine compartment &lt;ENG.&gt; has a power supply (battery) 1, a right-hand front lamp group 3, a left-hand front lamp group 5, an automatic transmission (hereinafter, referred to as A/T) position detection switch group 7, and an A/T shift switch group 9.
The above-mentioned front lamp groups 3, 5 each include a head lamp main a, a head lamp dimmer b, a clearance lamp c, a front turn signal (side marker lamp) d, and a side turn signal e.
The above-mentioned A/T position detection switch group 7 includes five detection switches each for detecting a shift position from among first (1-range), second (2-range), drive (D-range), neutral (N-range), reversal (R-range), and parking (P-range).
The above-mentioned A/T shift switch group 9 comprises three shift change switches covering 1 range - 2 range (1-2), 2 range - 3 range (2-3), 3 range - 4 range (3-4) and an oil temperature monitor switch (oil).
The dashboard section &lt;DASH&gt; includes a circuit breaker 11, a front lamp switch group 13, and a peripheral switch group 15.
The front lamp switch group 13 is provided with five operation switches denoted by the same symbols a, b, c, d, and e used for the lamp groups 3 and 5. That is to say, symbol a in the group 13 denotes a switch for the lamp main, symbol b in the group 13 denotes a switch for the dimmer, symbol c in the group 13 denotes a switch for the clearance lamp, symbol d in the group 13 denotes a switch for the front turn signal lamp, and symbol e in the group 13 denotes a switch for the side turn signal lamp.
The peripheral switch group 15 includes all switches and sensors not included in the engine or in the trunk, specifically, a parking brake switch Pa, an exhaust gas temperature sensor E, and a door switch Do.
The instrument panel &lt;INST&gt; includes an A/T position indicator 17, a warning lamp group 19, and a rear actuator switch group 21.
The above-mentioned A/T position indicator 17 is provided with six indicators displaying the shift gear positions 1, 2, D, N, R, and P corresponding to the above-described A/T position detection switch group 7.
The above-mentioned warning lamps 19 include a parking brake warning lamp Pa, an exhaust temperature warning lamp E, and a warning lamp Do indicating that a door is incompletely closed.
The above-described rear part actuator switch group 21 comprises a trunk lid opener solenoid switch T, fuel lid opener solenoid switch F, rear defogger resistor switch R, and power antenna motor switch A.
The trunk actuator group 23 comprises a trunk lid opener solenoid 23T, a fuel lid opener solenoid 23F, a rear defogger resistor 23R, and a power antenna motor 23A. In addition, an A/T (automatic transmission) control unit 25 is disposed in the trunk. A wire harness 27 extending the length of the vehicle interconnects these lamps, indicators, actuators, and so on.
It should be noted that various additional electrical appliances will be installed in the vehicle and serve either as information supply elements or information receiving elements. In the example given above of connections between conventional vehicle information supply elements and information receiving elements, the wire harness 27 is used to connect the various switches, sensors, etc with the corresponding indicators and actuators, as well as to the power supply 1 and short-circuit protector (circuit breaker) 11.
There is a problem in that the transmission and reception system which uses the wire harness as shown in FIG. 1 requires a relatively large harness under the recent circumstances in which the number of automotive electrical appliances is constantly increasing. As the diameter of each wire harness increases, the branching between harnesses becomes more complex so that overall manufacture and wiring also becomes more complex.
There is another problem in that since in the transmission and reception system using a wire harness as shown in FIG. 1, the signal transmission lines and high-voltage supply lines inevitably interfere, which reduces the reliability of signal transmission and reception despite noise-free countermeasures.
On the other hand, a multiplex transmission reception systems which solve the problems of the transmission and reception system described above have been proposed, for example, in Japanese Patent Application Unexamined Open No. Sho 50-27932 and Japanese Patent Application Unexamined Open No. Sho 57-208746.
FIG. 2 shows the basic structure of the multiplex transmission and reception system mentioned above applied to the vehicle.
In the conventional multiplex transmission and reception system shown in FIG. 2, the vehicle is divided into four regions, i.e., engine compartment, dashboard central section, instrument panel, and trunk, each position being provided with a dedicated multiplex transmission and reception unit 29, 31, 33, and 35 connected via a bus network 37 as shown in FIG. 2.
The network 37 may be of a loop type (refer to the Japanese Patent Application Unexamined Open No. 57-208746) in place of a bus type, or alternatively of a star type. In addition, normal vehicular wiring may be used for the trunk line 37 or alternatively a shielded cable or optical fiber may be used.
Each multiplex transmission and reception unit shown in FIG. 2 comprises a unit capable of transmitting and receiving related signals. Further a processing of signal transmission and reception is carried out in each multiplex transmission and reception system.
For example, suppose that lamp main switch a in the front lamp switch group 13 is turned on so that the turn-on signal is outputted to the transmission and reception unit 31 for the dashboard &lt;DASH&gt; via the line .lambda..sub.1. Then, the multiplex transmission and reception unit 31 reads the signal-level state on the line .lambda..sub.1 and sends same to a predetermined address corresponding to lamp main switch 13a, and sends a signal ordering both lamp mains a in the left and right main lamp groups 3, 5 to be turned on at a predetermined timing to another multiplex transmission and reception unit 29. The addressing and data transmission timing are carried out on the basis of an address clock signal in the form of an M-series time series code. As appreciated from FIG. 2, the transmission and reception units communicate between the addressed transmission memory and the addressed reception memory via a single line 37 and therefore the overall processing is complex.
The conventional multiplex transmission and reception system described above with reference to FIG. 2 has the following problems:
(1) Each multiplex transmission and reception unit must transmit and receive the data to and from each of the other positions and must carry out communications with all of the other multiplex transmission and reception units. Therefore, a high-level protocol and correspondingly complex structure are necessary.
(2) Each multiplex transmission and reception unit employs a high-level protocol. Therefore, if one of the multiplex transmission and reception units should fail, the symptoms of failure would appear at every unit, whereby failure diagnosis and trouble shooting would be difficult.
(3) The whole system must be connected by way of a high-level protocol. Therefore, as each multiplex transmission and reception unit is highly integrated, modification and alternation thereof are rather difficult, and thus the system lacks general-purpose utility.
(4) Each multiplex transmission and reception unit must be relatively large if a single standardized unit is to be mass-produced to provide general-purpose utility, in order to satisfy the needs of the largest station in the information transmission and reception system. Therefore, the cost of the whole system is increased.